1. Field of the Invention
The present invention is related to a method for inspecting overly shift defect during semiconductor manufacture and apparatus thereof, and more particularly, is related to a method for inspecting overlay shift between contact/via plugs and metal lines in a semiconductor device using charged particle beam imaging.
2. Description of Related Art
Overlay shift is a common defect which occurs during the manufacture of semiconductor devices (such as an integrated circuit). One of the major causes of the overlay shift defect is the misalignment of photolithography masks for forming two successive layers within a semiconductor device. FIG. 1 is a cross sectional view showing the overlay shift defect in a semiconductor device. As shown in FIG. 1, overlay shift defects could happen in various layers of a semiconductor device, for example at the location between a contact plug 104 and a first layer metal line 102 or the location between a via plug 108 and a second layer metal line 106. Because of overlay shifting, the formed metal lines fail to be aligned with the underneath contact/via plugs after etching. This would result in a high contact resistance between these elements. Such resistance can cause malfunction of the entire device, for example, a disconnected source/drain contact plug with the corresponding bit line can obstruct the operation of a DRAM device.
Another issue brought along by this type of defect is the manufacturing cost. As a semiconductor device is generally fabricated in a layer-by-layer fashion with one layer on top of another, a defective plug-to-contact layer should be reported immediately to stop the process so that further waste can be avoided.
Currently, the inspection of defects on a semiconductor sample is mostly carried out through charged particle beam imaging of the sample. FIG. 2 is a schematic illustration of a charged particle beam microscope system 200 according to the conventional art. A charged particle beam source 210 generates a charged particle beam, and then the charged particle beam is condensed and focused by a condenser lens module 220 and an objective lens module 230, respectively, to form a charged particle beam probe 240. The formed charged particle beam probe 240 then bombards the surface of a sample 295 secured on a stage 290. Charged particle beam probe 240 is controlled by a deflection module 250 to scan the surface of sample 295. After charged particle beam probe 240 bombards the surface of sample 295, secondary charged particles 260 are induced to emit from the sample surface along with other charged particles of beam probe 240 reflected by sample 295. These particles are then detected and collected by a detector module 270. Then, detector module 270 generates a detection signal 271 accordingly. An image forming module 280 coupled to detector module 270 then receives detection signal 271 and accordingly forms a charged particle microscopic image of sample 295. In one example, the charged particle is electron.
The overlay shift defect is, however, difficult to be examined by the existing charged particle beam inspection method/tools. Currently, monitoring of this defect is typically through human observation and interpretation of a top-down view charged particle microscopic image of the sample, and the result is more or less arbitrary and the accuracy is poor.
Therefore, it is desirable to have a method for reliably, in-time reporting the presence of the overlay shift defect after formation of a metal line on top of a contact/via plug, typically by an etching process, in a semiconductor device for the purpose of manufacture process control.